Japanese Patent Publication Tokkai Hei 4-78369 discloses an automatic transmission for an automotive vehicle in which a torque converter with a lock up clutch, and a toroidal continuously variable transmission are combined.
In the automatic transmission, in order to control the speed change ratio of the continuously variable transmission and engage and release the lock up clutch, a pressurized fluid is supplied from a single hydraulic pump. The fluid functions as a lubricating fluid for each lubricating portion of the continuously variable transmission.
In the toroidal continuously variable transmission, a power roller is disposed between an input disc and an output disc, the rotation in accordance with a contact friction there between is transferred and the speed change ratio is varied in a continuous manner in accordance with the angle of the incline of the power roller. In order to transmit high torque, a great contact pressure is applied between the power roller and the disc. As a result it is necessary to cool and lubricate these members by the application of considerable amounts of lubricating fluid. In this case, the lubricating fluid for the power roller and the disc portion can be divided into two lines. One is a fluid supply to the contact surface therebetween and another is a fluid supply to a bearing portion of the power roller.
The lubricating fluid from the pump is supplied via a torque converter pressure circuit for operating the lock up clutch, and a fluid cooler for cooling a lubricating fluid itself is interposed in the middle thereof. Since a pressure loss is generated when the lubricating fluid passes through the oil cooler, a pump having a great capacity is required in order to secure a supply amount of the lubricating fluid to the power roller under an high power operating condition.
Particularly, since high temperature working fluid enters the torque converter, after passing through the lock up clutch which is in a releasing state the fluid temperature becomes too high. Therefore lubricating and cooling performance deteriorates. Furthermore the durability of the torque converter is deteriorated, when lubricating fluid is supplied without passing through the oil cooler.